Counterfeiting of negotiable instruments, certificates, brand name products, and personal authentication media should desirably involve some difficulty. Therefore, it is often the case that such articles are provided with optical elements having a superior effect of preventing counterfeiting of articles.
Such optical elements are often provided with fine structures such as diffraction gratings, holograms, and lens arrays. Analysis of such fine structures is difficult. With this analysis difficulty, coupled with the necessity of using expensive equipment, such as an electron beam writer or the like, when being produced, such optical elements with fine structures exert a superior effect of preventing counterfeiting of articles.
The abovementioned optical element is provided with, for example, a formation layer for forming a diffraction structure serving as a diffraction grating or a hologram, and a metal layer formed on an uneven surface of the formation layer. The metal layer has a predetermined pattern and is positioned in a portion of the uneven surface. The metal layer is formed by, for example, forming a metal film by sputtering to array metal atoms substantially uniformly on the entirety of the uneven surface, and using photolithography to process the metal film into a predetermined shape (e.g., refer to PTL 1).